Process for welding tungsten ingots.



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C. A. PFANSTIEHI..

PROCESS FOR WELDING TUNGSTEN INGOTS.

APPLICATION FILED OCT-15,1915.

UNITED sTATEs PATENT OFFICE.

CARL PFANSTIEHL, 0F WAUKEGAN, ILLINOIS, ASSIGNOR TO PFANSTIEHL COMPANY,

i INC., OF NORTH CHICAGO, ILLINOIS, A. CORPORATION OE NEW YORK.

` PROCESS FOR WELDING TUNGSTEN INGOTS.

Specication of Letters Patent.

Patented May 28, 1918.

Application filed October 15, 1915. Serial No. 55,943.

To all whom it may concern.'

Be it known that I, CARL A. PFANSTIEHL, a citizen of the United States, and a resident of- Waukegan, in the county of Lake and State of Illinois, have invented certain new and useful Improvements in Processes for Welding Tungsten Ingots, of which the following is a clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of the specification. p

My invention relates to the art of Weld-y ing tungsten ingots, and more particularly to a process for treating compacted ingots of tungsten particles so that the particles of `tungsten will become fused or welded to one another to produce a solid rod of metallic tungsten. Myv present invention contemplates certain improvements ina process wherein line particles of metallic tungsten are compressed in a suitable die or mold to form an ingot of suiiicient stability to maintain its form While undergoing the fusing or Welding operation hereinafter described. In accordance with my present invention v the compacted rod, or ingot of tungsten particles is formed of such dimensions that it will act as a column with flat ends when placed between the jaws or electrodes of a suitable furnace, a preferred form of which is hereinafter fully described. The furnace which I prefer to utilize in carrying out my present process is provided with a pair of electrodes whose flat and parallel opposing surfaces are adapted to engage the tungsten ingot to be welded. The electrodes have preferably the cross sectional shape and area of the ingot to be welded and are preferably formed/of tungsten and preferably in part, at least, of tungsten carbid. The electrodes, or jaws, between which the ingot is clamped are provided with water cooled mountings and with connectors adapted to convey a heavy current of electricity to and from. the electrodes and thus through the ingot to be welded.

In carrying out my present process I contemplate maintaining the tungsten ingot under a longitudinal compressive stress while the said ingot is being subjected to the weldingor fusing operation. A convenient and highly satisfactory arrangement for accompl'ishing this end is to keep one, or both, of

the electrodes of the furnace under pressure, so that the jaws of the electrodes will be pressed into engagement with the ends of the ingot which is clamped in position between them. 4

In the particular furnace that I preferably employ in carrying out the process of my invention the electrodes and their mountings are supported in a water cooled endplate which serves as one wall of a hermetically sealed casing surrounding the electrodes and the ingot which is clamped between them. 'Ihe hood of the hermetically sealed casing is mounted on suitable trackwork such that it canbe withdrawn from the position in which it surrounds the electrodes and the ingot vto be welded, it being the part of the operator to withdraw this movable portion of the casing while inserting or removing an ingot from the electrodes between which it is fused or welded. After having inserted an ingot between the electrodes or jaws, the operator returns the movable hood of the casing to its normal position in which the ingot to be welded and the electrodes and their mountings are inclosed in a hermetically sealed chamber. The chamber may be exhausted so that the welding operation will occur n vacuo, or the casing may be filled with hydrogen or other inert gas. The electrodes between which the ingot 1s clamped may initially be formed of metallic tungsten substantially identical with that of the product of the welding process hereinafter described. I have found it desirable, howeverto sprinkle the tungsten electrodes, and particularly the engaging surfaces of the tungsten electrodes, with carbon in .one form or another, as, for example, in the form of graphite, before carrying out the .first or the first few of the welding operatlons. In my opinion, the carbon combines with the tungsten of the electrodes to produce a tungsten carbid which does not fuse or weld with the ingots undergoing treatment. Whatever the action of the carbon and tungsten may be, that is, whether chemical or purely physical, I prefer to refer to the resultant material as carborized tungsten. This preliminary treatment of the electrode apparently has the advantage also of preventing the temperature of the electrodes from rising to a high degree while the temperature of the ingot which is undergoing treatment may be raised practically raise its temperaturev to a point at which the tungsten particles will become fused orA welded to one another with the result that the ingot comes from the furnace 1n the form of a strong cohesive body of metalllc tungsten. In carrying out'the welding operation I have found it desirable to regulate the current which flows through the ingot so that its temperature will be raised gradually to a point considerably below that of fusion, or w'eldig,ad there maintained for several minutes. The current is then increased to such 'an extent that the tempera- 'ture ofthe ingot will be raised almost to the point at which the tungsten will melt and dow. This high degree of temperature may be maintained for such length of time as may be necessary to effect the complete welding of the tungsten particles. I have found in practice that the maintenance of this high temperature for one minute or less is sucient for the purposel' If the cross-section ,of the ingot undergoing treatment is of suicient area and of proper shape, it will act like a column with flat ends So that the pressure of the electrodes upon the ingot will maintain the ingot in alineinent between the electrodes even at the highest temperatures, thereby preventing the ingot from buckling or bending when brought to the high temperature necessary to effect the fusion or welding of the particles of which the ingot is'fcrmed.\Y

As has been hereinbefore pointed out an essential step in attainingI the results of my invention consists in subjecting the ingot under treatment to a`longitudinal compressive stress While the said ingot is undergoing the welding or fusing operation. I have found that when the ingot thus subjected to pressure from end to end has been heated to a certain temperature during the welding operation the length of the ingot suddenly becomes materially less without any increase in its transverse cross section. In an ingot of substantially square transverse cross section, three-eighths of an inch on a side and four inches in length, this sudden shortening of the ingot is often as great as one-sixteenth to one-eighth of an inch. The result of this sudden shortening is that the finished ingot is of great density and considerable malleability.

I have found also that if the electrodes of carborized tungsten are clamped firmly on all sides in rather massive mountings of copper or brass, which in turn are amply memset `behavior of the apparatus in this respect. I

believe that the water cooled mountings .of the electrodes act'toconvey the heat rapidly away from them. I believe, also, however,

that the fact that the electrodes are formed of carborized tungsten has some influence on the behavior of the apparatus. I have observed that when a tungsten ingot such as I have described, is clamped between the electrodes of the furnace and a current is conveyed through the ingot, the temperature of the ingot may bey raised to a high degree without raising the temperature of the carborized tungstenelectrodes to a point at which they are appreciably red. Even at the highest temperatures to which the ingot.

is brought in the welding operation, the electrodes are very markedly cooler than the ingot. rIhe temperatures at which these operations arel carried on are such that it is almost impossible to make accurate measurements of temperature. The temperatures are so high also that the ingot and the electrodes can be observed only when the inelosing chamber is provided with a heavy plateglass wall and when the observer is equipped with densely smoked or colored glasses. Such observation reveals the fact, however, that .there is a very sharp line of demarcation or difference between the temperature of the electrodes and the ingot undergoing treatment. The ingot can be made to glow at a white heat from end to end while the electrodes, even at their eXtremerends where they engage the ingot, will be at a temperature so low that they appear to be entirely black, at least by comparison with the white hot ingot which is clamped between them. It may be that the carborized tungsten has or assumes some peculiar property, as, for example, a decreased resistance tothe passage of electricity, or an increased conductivity of heat, which is accountable for the above stated phenomena, -or it may be that the incompleteness of the mechanical contact between the ingot andthe electrodes is such that the heat of the ingot is not conducted tov the electrodes ata rate' equal to that at which the water-cooled mountings conduct heat away from the electrodes. It may be that the proportions of the electrodes which I have employed have something to do with the success of this .type of furnace. I do know that the results hereiny described are readily attained in an apparatus which I have constructed and operated in accordance with this disclosure, and that equal results are not obtained when pure tungsten electrodes which have not'been treated w-ith carbon are used.

In that apparatus I have fused or welded ingots of substantially square cross section,

of an inch on a side and 4 inches in length. The electrodes of tungsten carbid have had cross-sections of the same size and shape as that of the ingot, and the electrodes have projected of an inch beyond their watercooled brass mountings. While I have no peenedv or hammered to an extent such that the cross-section of the rod can be changed from square'to octagonal.

In the accompanying drawings, Figure 1 is a vertical section of the water-cooled furnace whichl desirably employ in carrying out my present process.

Fig. 2 is a section on the line 2-2 of Fig.

1;*and

Eig. 3 is a section onI the line 3 3 of Fig. 1.

-The table or bench 10 has L shaped rails 11 and 12 secured thereon upon the upwardly projecting limb of which the guides 13,v attached to the. circumference of the outer shell 14 of the furnace, may -be freely slid along lengthwise of the L shaped rails 11 and 12.

The inclosing portion of the furnace is about eighteen inches in length and comprises in addition to the outer shell 14, heretofore referred to, an inner shell 15 similar in shape to the outer shell, but spaced therefrom to form a chamber through which water may be circulated by means of the intake tube 20 and discharge tube 21. These two cylindrical cups arev attached together at their open ends by means of an annulus 22 which also serves to seal the water chamber before mentioned. A gasket 24 of rubber, asbestos, or other suitable sealing liber is cemented to the annulus 22 and bears against the periphery of the inner wall 25 of the stationary head 26, which also embraces a water circulating chamber inclosed by the outer wall 27. This chamber is like'- wise provided vwith an inlet 28 and a dischar e opening 29 by means of which water, or oier cooling fluid, may be circulated as rapidly as found desirable to maintain the temperature of the metallic parts low enough that they may be handled.

Suitable means, herein shown as a -pair of levers 30`carrying rollers 31 and joined by a handle 32, is provided for ressing the movable portion f the tank rmly against the washer 24 and the stationary portion 26 to accomplish which the rollers 3l engage the cams 33 carried one on each side of the movable-portion of the tank. f

The electrodes and their supporting means comprise a main water cooled supporting conductor 35 horizontally mounted upon the block 36 located wholly outside of the furnace chamber. The conductor 35 is preferably formed of copper, brass, or other good heat conducting material, and extends through 'the stationary head 26 wherein it is sealed by the insulating gasket 37. That portion which projects within the furnace chamber must be of sulicient rigidity to need no support at its free end wliereon is carried an electrode support 39 of considerable bulk and provided with a chamber connected with the water circulating tubes 40 through the conductor 35 by means of tubular connections 41. The electrode proper 43 is preferably formed of carbonized tungsten and is clamped in the electrode support 39 by means of a movable plate 44, shown more clearly in Fig. 3. The plate 44 is preferably made of copper, as are also the screws 45, so that the heat from the electrode 43 will be readily conducted into the Water cooled electrode support 39.

The electrode support shown atthe right in Fig.4 1 is likewise mounted upon a water cooled conducting member 47 which also extends through the stationary head 26 of the furnace and is insulated therefrom by a washer 48. The outer and inner ends of conductor 47 are spaced from, but attached to, the water cooled conductor 35 by means of blocks of insulation 49 and 50, all of the parts being massivev so as to form a rigid structure and one which will readily conduct away heat. The end of the conductor 4 7 which projects within the furnace chamber has a dovetailed channel 51 formed therein within which is slidably mounted a block 52 against the rear end of which a spring 53 abuts. lThis movable carrier 52 is provided With electrode mounting means similaito that with which electrode block 39 is equipped, this means serving to hold the tungsten carbid electrode 55 in place by means of screws 57. Although the block 52, and parts carried thereby, are in electrical connection with the conductor 47 the possible resistance of the sliding engagement is reduced by means of a flexible conductor 53 formed of braided or woven copper wire. This has been found necessary in order that the block 52 may be so freely mounted in its guide channel 51 that the spring 53 will readily maintain the tungsten carbid electrode 55 in contact with the end of the tung sten rod 56 despite the expansion and contraction of the tungsten rod or ingot during the welding operation. The pressure of the spring 53 must be sufficient that the parallel ends of the electrodes 43 and 55 will constantly act upon the parallel ends of the iso tungsten ingot 56 in a manner which will tend to prevent the sagging of the ingot when heated almost to Jthe melting point, and also permit and effect the shortening of the ingot with a resulting increased density when the ingot has been heated to the critical temperature at which this phenomenon occurs.

A peculiar property of tungsten is that when heated barely below the temperature at which it becomes fluid it will withstand a considerable compression, but at this point has practically no tensile strength. Obviously, the arrangement herein described takes advantage of this inherent quality of tungsten.

Since to weld an ingot of the size which I prefer to use, which is about one-sixteenth of a square inch in cross section, requires a maximum current of about 2000 amperes which must be brought gradually to that quantity and again gradually to a minimum of substantially 800 amperes, I have found it convenient and economical to use alternating current and to control this current by means of a variable impedance, herein diagrammaticallyl illustrated at 58, which is connected in circuit with the primary of a suitable transformer 59, and any suitable source of alternating current. 'Ihe low resistance secondary of the transformer 59 is connected directly to the outer terminals 417 and A35..

In order that the welding operation may be carried 'on without oxidization .which would rapidly occur at the high temperature to which the tungsten ingot must be raised, I have provided inlet and exit connections 62 and 63, by means of which a supply of hydrogen, or other inert gas, may be conducted to and from the furnace chamber. In the drawings I have illustrated somewhat diagrammatically a preferred arrangement for supplying hydrogen `to. the furnace chamber. `At 64C'is illustrated a hydrogen tank, or V other source of hydrogen supply, connected with a three-way cock 65. At 66 is illustrated a rubber gas bag which may be provided with a suitable woven sheath 67 if desired. The bag 66 is also connected with the cock 65. A suitable conduit 68 extends from the cock to the hydrogen inlet 62 of the furnace chamber. cock 65, which is of any suitable Well-known construction, is designed when in one position to adord communication between the hydrogen tank 64 and the gas bag 66, and when in another position to adord communication between the gas bag and the furnace chamber. Thus, a measured quantity of hydrogen may be readily supplied to the furnace chamber by manipulating the cock 65 to permit the gas bag to fill and then 'turning thecock to shut olf communication with the hydrogen supply and establish com- The three-way p meneer munication between the gas bag and the furnace chamber. Obviously, the operation may be carried on n vacuo if desired, in whlch case the tubes 62 and 63 would be suitably connected for exhausting the furnace chamber. I prefer, however, to operate in a medium of hydrogen since the heat conductivity of the hydrogen aids in cooling the ingot after welding so that it may be handled more quickly, and the second operation, therefore, more speedily started.

Although I have referred to the electrodes as constructed of carborized tungsten, I am not sure that the tungsten and carbon are in chemical union. 'The`substance may be formed, as pointed out, by heating tungsten upon which powdered graphite has been sprinkled. Satisfactory results may be obtained by constructing the electrodes of pure tungsten and then applying carbon in powdered form at the time of the first welding operation. y

Although the several steps constituting my process, as hereinafter claimed, have, as a matter of convenience, been described in connection with the preferred form of apparatus I appreciate the fact that this particular apparatus need not necessarily lhe employed in carrying out my process for welding tungsten ingots. -The following -claims are drawn to cover the process, which may be carried out in various ways and with various heating apparatuses.

Having thus describedmy invention what I claim as new and desire to secure by United `States Letters Patent is:

1. rllhe improvement in the art of sintering tungsten ingots which consists in's'ubjecting the whole of an ingot of compressed tungsten particles to .a longitudinal compressive stress and heating the ingot while it is thus subjected to a longitudinal cornpressive stress.

2. The process which consists in heating an entire ingotl of compressed tungsten particles to sintering temperature while the said ingot is being subjected to a longitudinal compressive stress applied at lits extremities.

3. The process which consists'in heating an ingot of compressed tungsten particles to sintering temperature while the entire ingot is being subjected to a compressive stress.

4. The process which consists in heatingv ingot is held in suspension between electrodes of the same cross section as the ingot itself and which exert a yielding compressive stress upon the opposite extremities of said ingot.

6. The process which consists in clamping a tungsten ingot between a air of carborized tungsten electrodes abuttmg against the opposite ends .of the ingot, and passlng an electric current threugh the electrodes and 10 ingot.

In Witness whereof, I hereunto subscribe my name this lst day of October, A. D. 1915.

CARL A. PFANSTIEHL.

Witnesses:

A. G. MGCALEB, H. A. NEIBURGER. 

